Cobalt Mining Legacy

Water Pollution in the Cobalt Area

The study of the problem of water pollution in Cobalt dates back to 1967, when the Ontario Water Resources Commission sampled lakes and streams in the area. Various studies of water pollution in the area are described in more detail in “Environmental Studies in Cobalt”.

Water Pollution in Lakes and Streams

Arsenic from tailings, waste rock and mine workings has been leaching into the lakes and streams around Cobalt for a century. As a result, the surface waters in Cobalt contain some of the highest concentrations of arsenic in water anywhere in Canada.

Arsenic occurs in all lakes and streams in the Cobalt area. The average arsenic concentrations range from 0.004 parts per million (ppm) in Sasaginaga Lake near the Cobalt town water intake to 17.8 ppm for a small stream draining the some tailings on Nip Hill. In comparison, the Canadian Water Quality Guideline for arsenic for the protection of aquatic life is 0.005 ppm. This concentration is exceeded in all lakes and streams sampled in the area except Sasaginaga Lake.

According to an Environment Canada report prepared under the Canadian Environmental Protection Act, the highest reported concentrations of arsenic in surface waters in Canada were found in lake water samples collected in the Yellowknife area, an area well known for its high profile arsenic problems due to gold mining dating to the 1940's. In the mid-1970s concentrations ranging from 0.700 to 1.500 ppm of arsenic, and 1.5 to 5.5 ppm of arsenic were reported in two small Yellowknife area lakes – Keg Lake and Kam Lake – the lakes most heavily impacted by mining. Data from the early 1990's suggested that arsenic concentrations in these lakes had dropped to about 0.545 and 0.645 ppm, respectively.

In comparison with these data from Yellowknife, the average concentration of arsenic in Cobalt Lake in 15 samples collected at various locations in the lake from 1991 to 1997 was 0.720 ppm. That concentration is almost 150 times the guideline for arsenic for the protection of freshwater aquatic life. Downstream, in Mill Creek, arsenic concentrations are even higher.

The highest concentrations of arsenic in surface water in the Cobalt area in studies done between 1991 and 1997 were in streams draining the tailings from the Nipissing low grade mill (average of 5.340 ppm in 6 samples) and the Nipissing high grade mill (average of 17.867 ppm in 8 samples).

As illustrated in the above map, there are significant increases in arsenic concentration from points upstream of the mining areas to points further downstream. This emphasizes that tailings and waste rock are the most important sources of water pollution in the area. However, it is important to remember that arsenic occurs naturally in the rocks of the Cobalt area, and it is probable that lakes and streams in the area, especially Cobalt Lake, always contained higher than normal amounts of arsenic.

»Download compilation of arsenic data for 1991 to 1997

Not only are the concentrations of arsenic in the surface waters around Cobalt high, but the total amount of arsenic released is also high. In fact, the Cobalt area is one the largest sources in Canada of releases of arsenic to surface water. Estimates of the amount of arsenic released each year into Lake Temiskaming range from 10,000 to 18,000 kilograms. These estimates are based on measured concentrations of arsenic at a location in Farr Creek near North Cobalt, and the measure flow rate of the creek at the same location.

To put this amount in perspective, this means that more arsenic is being released from the mines around Cobalt than was released from all of the metal mines operating in Canada in 2003 – COMBINED – according to data reported to Environment Canada under Canada's Metal Mining Effluent Regulations!

Arsenic is the main contaminant of concern in the Cobalt area, but it is not the only metal polluting lakes and streams in the area. Nickel and cobalt are also found in local lakes and streams. Mercury has also been found in some water samples, and there is mercury in the fish in many of the lakes in the area. A memo from the Ontario Ministry of Natural Resources in 1994 suggests that the mercury concentrations in fish from Cobalt Lake are among the highest in the province.

Water Pollution in Groundwater

At least two studies have looked at the concentrations of arsenic and other contaminants in groundwater collected from wells in the area.

One study, conducted in 1977, identified arsenic in a number of wells in the area. Many of these wells were later replaced with new wells. A study completed in 1993 showed that the water in 25 of 26 wells sampled did not contain harmful concentrations of arsenic or other metals.

However, one well, in a campground on the shores of Lake Temiskaming, had exceptionally high concentrations of arsenic, averaging almost 7 ppm. The maximum acceptable concentration of arsenic in drinking water is 0.025 ppm, so the concentrations of arsenic in water from that well were almost 300 times the safe limit for drinking water. The Temiskaming Health Unit closed this well in the late 1990s.

It is difficult to know if the arsenic in this well was the result of mining in the area, since the rock unit that the well took water from has long been known to contain very high concentrations of arsenic.